A brushless direct current (BLDC) motor typically includes a rotor containing one or more permanent magnets and a stator with electromagnets that are dynamically switched. A controller controls the motor speed and commutation by modulating the width of pulses applied to switches in each motor phase driver. In a typical BLDC motor startup sequence, the controller drives the motor like a stepper motor because there is no significant back EMF at zero or low speed to use in making zero-crossing commutation decisions. Thus the motor is initially commutated very slowly, and then its velocity is increased by reducing the commutation time while the PWM duty cycle is increased over time to boost the applied motor voltage and to keep the current constant. This startup sequence is typically implemented using a table of duty cycles and another table timing delays for each commutation for a typical configuration and load.
The use of the same reference symbols in different drawings indicates similar or identical items. Unless otherwise noted, the word “coupled” and its associated verb forms include both direct connection and indirect electrical connection by means known in the art, and unless otherwise noted any description of direct connection implies alternate embodiments using suitable forms of indirect electrical connection as well.